Determining the crankshaft angle is one of the central tasks for controlling internal combustion engines. Conventional approaches use incremental sensors on the crankshaft and the camshaft. The typical sensor wheels having increment marks make cooperation of the crankshaft and camshaft sensors possible for determining the crankshaft angle. Another improvement on the control of an internal combustion engine is achieved if the crankshaft position is detected accurately when the internal combustion engine is stopped. This makes it possible to considerably speed up the restart of the internal combustion engine and to achieve a positive effect on comfort and exhaust gas emission. When the internal combustion engine is stopped, an oscillation of the crankshaft may occur, i.e., an alternating movement in both directions until standstill is reached. In general, sensors currently used in internal combustion engines are unable to recognize the direction of rotation and are therefore unable to reliably determine the absolute position of the crankshaft.
In principle, it is possible to add a direction of rotation recognition to the crankshaft angle sensor. At least two sensor elements are to be appropriately situated in a sensor housing for this purpose. The direction of rotation may be ascertained from the timing of the sensor signals. Sensors of this type having two sensor elements (transducer elements) are known as differential sensors. Sensors without direction of rotation recognition have one output, i.e., a total of three terminals (supply voltage, ground, signal output). Sensors having direction of rotation recognition often contain two signal outputs. In one specific embodiment, the signals of both sensor elements are output; in another specific embodiment, one output is provided for the tooth frequency information and the other output is provided for the direction of rotation information. It is furthermore conventional to select a signal encoding which transmits the tooth frequency and direction of rotation via a single terminal. A signal encoding of this type is performed via the signal pulse length. The signal is thus pulse-width modulated and contains two different pulse lengths PL1 and PL2, which represent the clockwise and counterclockwise rotation, respectively. Every time a rising tooth edge passes by, the output of pulse form PL1 or PL2 is triggered, depending on the direction of rotation.
It is problematic that, in the event of a direction of rotation reversal, while a tooth or a tooth gap passes the sensor, depending on the position of the direction of rotation reversal point, a systematic error may occur in the incremental angle determination.